Method for producing C9-alcohols and method for the integrated production of C9-alcohols and C10-alcohols

ABSTRACT

A process for preparing C 9 -alcohols comprises a) providing a C 4 -hydrocarbon stream comprising butene and butane; b) subjecting the C 4 -hydrocarbon stream to oligomerization over an olefin oligomerization catalyst and fractionating the resulting reaction mixture to give an octene-containing stream and a butene-depleted C 4 -hydrocarbon stream; c) subjecting the butene-depleted C 4 -hydrocarbon stream to steam reforming or partial oxidation to give carbon monoxide and hydrogen; d) hydroformylating the octene-containing stream by means of carbon monoxide and hydrogen in the presence of a hydroformylation catalyst to form C 9 -aldehydes, where the carbon monoxide used and/or the hydrogen used originate at least in part from step c); and e) catalytically hydrogenating the C 9 -aldehydes by means of hydrogen. In a variant of the process, part of the butenes present in the C 4 -hydrocarbon stream are hydroformylated to form C 5 -aldehydes, these are subjected to an aldol condensation and the product of the aldol condensation is hydrogenated to form C 10 -alcohols. The process allows the C 4 -hydrocarbon stream used to be substantially utilized as material.

The present invention relates to a process for preparing C₉-alcohols andalso to a process for the integrated preparation of C₉-alcohols andC₁₀-alcohols.

Fossil fuels and the hydrocarbons obtained therefrom have a doublefunction in industrial synthesis. They serve firstly as energy sourcesand secondly as raw materials for chemical products. It is frequentlycustomary to burn hydrocarbons obtained as by-products in industrialsynthesis or depleted in specific products of value in order to maketheir energy content available. There is at present a tendency toreplace fossil fuels in the energy sector and thus to secure rawmaterials supply in the long term at a given supply of fossil rawmaterials. To achieve this, it is necessary to use as much as possibleof the components present in the hydrocarbons obtained from fossil rawmaterials as materials. A difficulty is that hydrocarbon streams areusually obtained as poorly defined mixtures of variable composition inindustrial synthesis. The utilization as materials of the components ofvalue present therein frequently founders on the disproportionately highcost of purification or fractionation. It is necessary to deviseintegrated processes in which the by-products of one process step can beutilized as materials in a further process step without complicatedfractionation being required.

It is known that C₄ fractions which are available in large quantitiesboth from FCC plants and from steam crackers and consist essentially ofa mixture of butene and butane can be subjected to an oligomerizationreaction to produce butene oligomers, in particular octenes. Such aprocess is described, for example, in DE 4 339 713. This reaction givesthe butene oligomers and a butene-depleted C₄-hydrocarbon stream inwhich the butenes are diluted by so much butane that the oligomerizationof the butenes still present therein is no longer practical.

The octenes are usually hydroformylated to form C₉-aldehydes and thenhydrogenated to give C₉-alcohols. The C₉-alcohols have valuableproperties as plasticizer alcohols.

The production of synthesis gas by steam reforming or partial oxidationof hydrocarbons is also known (cf. Weissermel, K. and Arpe H. -J.,“Industrielle organische Chemie”, VCH, 4th Edition, 1994, pages 19-24.

In Sb. Nauchn. Tr.—Vses. Nauchno-Issled Inst. Pererab. Nefti (1981), 39,11-20, Gusev I. N. et al. report the preparation of hydrogen bycatalytic steam reforming of refinery gases comprising hydrogen,C₁₋₄-alkanes and about 20% of alkenes. An upstream hydrogenation step isdescribed as being advantageous.

JP 52132-004 describes the preparation of a gas comprising from 50 to 95mol % of H₂, from 1 to 50 mol % of CO, <25 mol % of CO₂ and <25 mol % ofmethane by treating a hydrocarbon with an NiO catalyst in the presenceof steam.

In Nippon Gasu Kyokaishi (1978), 31(8), 21-9, Yokoyama, A. reportsresults on the catalytic reforming of C₄-alkanes and a fraction having ahigh content of C₄-alkanes and C₄-alkenes.

It is an object of the present invention to provide a process forpreparing C₉-alcohols and a process for preparing C₉-alcohols andC₁₀-alcohols which start out from C₄-hydrocarbons and allow verysubstantial utilization of the feed hydrocarbons as materials.

We have found that this object is achieved by using the butene-depletedC₄-hydrocarbon stream obtained in butene oligomerization as startingmaterial for the preparation of synthesis gas which can be employed forhydroformylation of the octenes obtained by butene dimerization to formC₉-aldehydes and/or of butene to form C₅-aldehydes.

The present invention accordingly provides, in a first aspect, a processfor preparing C₉-alcohols, which comprises

a) providing a C₄-hydrocarbon stream comprising butene and butane;

b) subjecting the C₄-hydrocarbon stream to oligomerization over anolefin oligomerization catalyst and fractionating the resulting reactionmixture to give an octene-containing stream and a butene-depletedC₄-hydrocarbon stream;

c) subjecting the butene-depleted C₄-hydrocarbon stream to steamreforming or partial oxidation to give carbon monoxide and hydrogen;

d) hydroformylating the octene-containing stream by means of carbonmonoxide and hydrogen in the presence of a hydroformylation catalyst toform C₉-aldehydes, where the carbon monoxide used and/or the hydrogenused originate at least in part, e.g. to an extent of more than 50%,preferably to an extent of more than 80%, in particular completely, fromstep c); and

e) catalytically hydrogenating the C₉-aldehydes by means of hydrogen.

The hydrogen used in step e) preferably originates at least in part,e.g. to an extent of more than 50%, preferably to an extent of more than80%, in particular completely, from step c).

The “butene-depleted C₄-hydrocarbon stream” is depleted in butenecompared to the C₄-hydrocarbon stream used. The amount of butenespresent is reduced by a proportion corresponding to the buteneconversion in the oligomerization. In general, the butene content of thebutene-depleted C₄-hydrocarbon stream is decreased by from 70 to 99%,usually from 80 to 95%, compared to the C₄-hydrocarbon stream used. Thebutene-depleted C₄-hydrocarbon stream comprises, for example, from 5 to70 mol %, usually from 5 to 45 mol %, of butene, with the remainderbeing essentially butane.

The present invention also provides, in a second aspect, a process forthe integrated preparation of C₉-alcohols and C₁₀-alcohols, whichcomprises

a) providing a C₄-hydrocarbon stream comprising butene and butane;

b) hydroformylating the C₄-hydrocarbon stream by means of carbonmonoxide and hydrogen to form C₅-aldehydes, so as to give a firstbutene-depleted C₄-hydrocarbon stream;

c) subjecting the C₅-aldehydes to an aldol condensation; and

d) catalytically hydrogenating the products of the aldol condensation bymeans of hydrogen to form C₁₀-alcohols;

e) subjecting the first butene-depleted C₄-hydrocarbon stream tooligomerization over an olefin oligomerization catalyst andfractionating the resulting reaction mixture to give anoctene-containing stream and a second butene-depleted C₄-hydrocarbonstream;

f) hydroformylating the octene-containing stream by means of carbonmonoxide and hydrogen in the presence of a hydroformylation catalyst toform C₉-aldehydes;

g) catalytically hydrogenating the C₉-aldehydes by means of hydrogen;

h) subjecting the second butene-depleted C₄-hydrocarbon stream to steamreforming or partial oxidation to give carbon monoxide and hydrogenwhich are recirculated at least in part to step b) and/or step f).

The hydrogen used in step d) and/or in step g) preferably originates atleast in part, e.g. to an extent of more than 50%, preferably to anextent of more than 80%, in particular completely, from step d).

The “first butene-depleted C₄-hydrocarbon stream” is depleted in butenecompared to the C₄-hydrocarbon stream used, and the “secondbutene-depleted C₄-hydrocarbon stream” is depleted in butene compared tothe first butene-depleted C₄-hydrocarbon stream. In general, the butenecontent of the first butene-depleted C₄-hydrocarbon stream is reduced byfrom 25 to 50%, and that of the second butene-depleted C₄-hydrocarbonstream is reduced by from 70 to 99% compared to the firstbutene-depleted C₄-hydrocarbon stream. The first butene-depletedC₄-hydrocarbon stream comprises, for example, from 30 to 60 mol % ofbutene and the second butene-depleted C₄-hydrocarbon stream comprises,for example, from 0.3 to 20 mol % of butene, with the remainderessentially butane.

C₄-hydrocarbon streams suitable as starting material comprise, forexample, from 50 to 99 mol %, preferably from 60 to 90 mol %, of butenesand from 1 to 50 mol %, preferably from 10 to 40 mol %, of butanes. Thebutene fraction preferably comprises from 40 to 60 mol % of 1-butene,from 20 to 30 mol % of 2-butene and less than 5 mol %, in particularless than 3 mol %, of isobutene (based on the butene fraction). Aparticularly preferred starting material is raffinate II, which is anisobutene-depleted C₄-fraction from an FCC plant or a steam cracker.Raffinate II has the following typical composition:

i-,n-butane 26 mol % i-butene 1 mol % l-butene 26 mol % trans-2-butene31 mol % cis-2-butene 16 mol %

If diolefins or alkynes are present in the C₄-hydrocarbon stream, theyare preferably removed to leave a residual concentration of less than 10ppm, in particular less than 5 ppm, prior to the oligomerization. Theyare preferably removed by selective hydrogenation, e.g. as described inEP-81 041 and DE-1 568 542. In addition, oxygen-containing compoundssuch as alcohols, aldehydes, ketones and ethers are also preferablysubstantially removed. For this purpose, the C₄-hydrocarbon stream canadvantageously be passed over an adsorbent, e.g. molecular sieves, inparticular molecular sieves having a pore diameter of from >4 Å to 5 Å.

The individual steps of the process of the present invention are knownper se and their specific configuration is not a subject matter of thepresent invention. The individual steps are described in more detailbelow with the aid of illustrative or preferred embodiments.

Oligomerization

A number of processes are known for the oligomerization, in particulardimerization, of lower olefins such as butenes. Each of the knownprocesses is suitable in principle for carrying out the buteneoligomerization step of the process of the present invention.

The oligomerization of olefins can be carried out in the presence ofhomogeneous or heterogeneous catalysts. An example of a homogeneouslycatalyzed process is the DIMERSOL process. In the DIMERSOL process (cf.Revue de l'Institut Frangais du Petrol, Vol. 37, No. 5,September/October 1982, page 639ff), lower olefins are dimerized in theliquid phase. Suitable precursors of the catalytically active speciesare, for example, (i) the system π-allyl-nickel/phosphine/aluminumhalide, (ii) Ni(O) compounds in combination with Lewis acids, e.g.Ni(COD)₂+AX_(n) or Ni(CO)₂(PR₃)+AX_(n), or (iii) Ni(II) complexes incombination with alkylaluminum halides, e.g. NiX₂(PR₃)₂+Al₂Et₃Cl₃ orNi(OCOR)₂+AlEtCl₂ (where COD=1,5-cyclooctadiene, X=Cl, Br, I; R=alkyl,phenyl; AX_(n)=AlCl₃, BF₃, SbF₅ etc.). A disadvantage of thehomogeneously catalyzed processes is the difficulty of removing thecatalyst.

These disadvantages do not exist in heterogeneously catalyzed processes.In these processes, an olefin-containing stream is generally passed atelevated temperature over a fixed bed of the heterogeneous catalyst.

A widespread industrial process is the UOP process using H₃PO₄/SiO₂ in afixed bed (cf., for example, U.S. Pat. No. 4,209,652, U.S. Pat. No.4,229,586, U.S. Pat. No. 4,393,259). In the Bayer process, acid ionexchangers are used as catalyst (cf., for example, DE 195 35 503, EP-48893). WO 96/24567 (Exxon) describes the use of zeolites asoligomerization catalysts. Ion exchangers such as Amberlite are alsoused in the Texas Petrochemicals process (cf. DE 3 140 153).

The dimerization-of lower olefins using alkali metal catalysts is alsoknown (cf. Catalysis Today, 1990, 6, p. 329ff).

For the present purposes, preference is given to carrying out the buteneoligomerization over a heterogeneous nickel-containing catalyst. Theheterogeneous, nickel-containing catalysts which can be used may havedifferent structures, with preference being given to catalystscomprising nickel oxide. Catalysts known per se, as are described in C.T. O'Connor et al., Catalysis Today, Volume 6 (1990), pages 336-338, canbe used. In particular, supported nickel catalysts are used. The supportmaterials can be, for example, silica, alumina, aluminosilicates,aluminosilicates having sheet structures and zeolites, zirconium oxide,which may have been treated with acids, or sulfated titanium dioxide.Particularly useful catalysts are precipitated catalysts which areobtainable by mixing aqueous solutions of nickel salts and silicates,e.g. sodium silicate with nickel nitrate, and possibly aluminum saltssuch as aluminum nitrate, and calcining the precipitate. It is alsopossible to use catalysts which are obtained by intercalation ofNi²⁺ions into natural or synthetic sheet silicates, e.g.montmorillonites, by means of ion exchange. Suitable catalysts can alsobe obtained by impregnation of silica, alumina or aluminosilicates withaqueous solutions of soluble nickel salts, e.g. nickel nitrate, nickelsulfate or nickel chloride, and subsequent calcination.

Particular preference is given to catalysts which consist essentially ofNiO, SiO₂, TiO₂ and/or ZrO₂ and, if desired, Al₂O₃. They lead todimerization occurring preferentially over the formation of higheroligomers and give predominantly linear products. The most preferredcatalyst is one which comprises as essential active constituents from 10to 70% by weight of nickel oxide, from 5 to 30% by weight of titaniumdioxide and/or zirconium dioxide, from 0 to 20% by weight of aluminumoxide and silicon dioxide as balance. Such a catalyst is obtainable byprecipitation of the catalyst composition at a pH of from 5 to 9 byadding an aqueous solution of nickel nitrate to an alkali metal waterglass solution containing titanium dioxide and/or zirconium dioxide,filtration, drying and heat treatment at from 350 to 6505C. For detailsof the production of these catalysts, reference may be made to DE 4 339713. The disclosure of this publication and the prior art cited thereinis fully incorporated by reference.

The catalyst is preferably in pelletized or granulated form, e.g. in theform of pellets having, for example, a diameter of from 2 to 6 mm and aheight of from 3 to 5 mm, rings having, for example, an externaldiameter of from 5 to 7 mm, a height of from 2 to 5 mm and a holediameter of from 2 to 3 mm, or extrudates of various lengths having adiameter of, for example, from 1.5 to 5 mm. Such shapes are obtained ina manner known per se by tableting or extrusion, usually using atableting aid such as graphite or stearic acid.

The oligomerization over the heterogeneous, nickel-containing catalystis preferably carried out at from 30 to 280° C., in particular from 30to 140° C. and particularly preferably from 40 to 130° C. It ispreferably carried out at a pressure of from 10 to 300 bar, inparticular from 15 to 100 bar and particularly preferably from 20 to 80bar. The pressure is advantageously set so that the C₄-hydrocarbonstream is in the liquid or supercritical state at the temperatureselected.

The C₄-hydrocarbon stream is advantageously passed over one or morefixed-bed catalysts. Suitable reaction apparatuses for bringing theC₄-hydrocarbon stream into contact with the heterogeneous catalyst areknown to those skilled in the art. Examples of suitable apparatuses areshell- and -tube reactors or shaft ovens. Owing to the lower capitalcosts, shaft ovens are preferred. The oligomerization can be carried outin a single reactor, in which case the oligomerization catalyst can bearranged in one or more fixed beds in the reactor. As an alternative,the oligomerization can be carried out using a reactor cascadecomprising a plurality of reactors, preferably 2 reactors, connected inseries, in which case the oligomerization of the C₄-hydrocarbon streamis carried out only to partial conversion during passage through thereactor or reactors upstream of the last reactor of the cascade and thedesired final conversion is achieved only during passage of the reactionmixture through the last reactor of the cascade.

After leaving the reactor or the last reactor of a cascade, the reactionmixture is fractionated into an octene-containing stream, possiblyhigher oligomers and a butene-depleted C₄-hydrocarbon stream. Theoctene-containing stream preferably comprises more than 97% by weight ofisomeric octenes; in particular, it consists essentially entirely ofisomeric octenes.

The above description of olefin oligomerization applies analogously tothe use of the first butene-depleted C₄-hydrocarbon stream according tothe second aspect of the invention.

Steam Reforming

In steam reforming (allothermal steam cracking), hydrocarbons arecracked catalytically in the presence of H₂O to give a mixture of carbonmonoxide and hydrogen, viz. synthesis gas. The heat required for theendothermic reaction is supplied from outside. The chemical reaction insteam reforming can be described by the following overall equation:

CH_(x)+H₂O→CO+H₂+x/2 H₂

From this equation, it can be seen that the contribution of thehydrocarbon feedstock to the amount of H₂ formed increases with itshydrogen content. A butene-depleted C₄-hydrocarbon stream obtained inthe process of the present invention has, for example, a typicalcomposition of 19 mol % of butene and 81 mol % of butane. In this case,the butene-depleted C₄-hydrocarbon stream has an average empiricalformula of C₄H_(9.62), so that the reaction is:

C₄H_(9.62)+4 H₂O→4 CO+8.81 H₂

The H₂/CO molar ratio of the synthesis gas obtained is thus 2.2:1.

The hydroformylation step of the process of the present invention, whichis described in more detail further below, can be represented by thefollowing equation:

C₈H₁₆+CO+H₂→C₈H₁₇—CHO

and the hydrogenation step by the following equation:

C₈H₁₇—CHO+H₂→C₈H₁₇—CH₂OH

It can be seen that the combination of the hydroformylation andhydrogenation steps requires hydrogen and carbon monoxide in a molarratio of 2:1. As shown above, the synthesis gas obtained by steamreforming of the butene-depleted C₄-hydrocarbon stream has awell-matched H₂:CO molar ratio.

Steam reforming is generally carried out by continuously reacting amixture of hydrocarbon and steam in externally heated tubes oversuitable catalysts, e.g. nickel catalysts, at atmospheric orsuperatmospheric pressure and temperatures of, for example, from 700 to950° C. Many parallel, catalyst-filled tubes, usually of chromium-nickelsteel, are installed vertically in refractory-lined reactors in such away that they can expand freely. The tube diameter is, for example, from15 to 20 cm and the heated tube length is 9 m. The tubes are heated fromthe outside by means of burners. For heating the tubes, it is possibleto use an external fuel or preferably part of the butene-depletedC₄-hydrocarbon. To produce low-methane synthesis gas, the gas from themultitube furnace can be passed into an after-combustion furnaceconfigured as a shaft furnace.

Suitable catalysts for steam reforming are described, for example, inMax Appl, Modern Production Technologies, published by Nitrogen, BritishSulphur Publishing, 1997, p. 10ff.

The CO₂ formed as by-product can advantageously be separated off (seebelow) and recirculated wholly or in part to the steam reformer. Therecirculated carbon dioxide reacts with the hydrocarbons CH_(x) to formusable hydrogen and carbon monoxide.

In a preferred embodiment, the steam reforming step includes partial orcomplete hydrogenation of the butene-depleted C₄-hydrocarbon stream inorder to convert the butene still present wholly or partly into butanebefore the C₄-hydrocarbon stream is introduced into the reformer. Thebutene content of the stream is preferably reduced to less than 5 mol %,in particular to less than 1 mol %, in this way. The hydrogenationavoids the risk of deposition of carbon on the reforming catalyst, whichis possible in the case of a high residual butene content or a highspace velocity over the catalyst. Although the deposition of carbon canalso be reduced by means of higher steam/hydrocarbon ratio, this is atthe expense of the thermal efficiency and the carbon monoxide content ofthe final gas. The prior hydrogenation of the butene-depletedC₄-hydrocarbon stream is advantageously carried out using recirculatedhydrogen gas. Hydrogen can be isolated from the synthesis gas formed insteam reforming by, for example, pressure swing adsorption orlow-temperature distillation. Such processes are described, for example,in Max Appl, loc. cit., p. 108ff. Suitable plants for producingsynthesis gas by steam reforming are described, for example, in MaxAppl, loc. cit., p. 7ff.

Suitable catalysts for the complete or partial hydrogenation of thebutene-depleted C₄-hydrocarbon stream are, for example, nickel oxide,cobalt oxide and/or molybdenum oxide on support materials comprisingaluminum oxide.

In a preferred embodiment, a prereforming step is carried out prior tosteam reforming or between hydrogenation and steam reforming. Theprereformer operates at a lower temperature than the actual steamreformer. Typical operating temperatures of the prereformer are from 400to 550° C. For this purpose, the mixture of hydrocarbon and steam ispassed over the fixed bed of a prereforming catalyst at, for example,530° C. In the prereformer, higher hydrocarbons, predominantly C₄building blocks, are cracked into C₂ and C₁ building blocks. Owing tothe endothermic reaction, a pressure drop of, for example, from 60 to70° C. occurs in the catalyst bed. The gas leaving the prereformer issubsequently brought back to the required reformer inlet temperature.

The prereforming step can be carried out in a manner analogous to thatdescribed, for example, in H. Jockel, B. Triebskorn: “Gasynthan processfor SNG”, Hydrocarbon processing, January 1973, pp. 93-98. A suitableprereforming catalyst is a supported nickel oxide catalyst as sold byBASF AG, Ludwigshafen, under the designation G 1-80.

Partial Oxidation

Synthesis gas can likewise be prepared by reacting hydrocarbons withsubstoichiometric amounts of oxygen. The preparation of synthesis gas bypartial oxidation can be described by the following equation:

CH_(x)+½ O₂→CO+x/2 H₂

For a typical empirical formula of the butene-depleted C₄-hydrocarbonstream of C₄H_(9.62), this becomes:

C₄H_(9.62)+2 O₂→4 CO+4.81 H₂

The H₂/CO molar ratio of the synthesis gas obtained is 1.2:1. Synthesisgas of this composition is well-suited to carrying out hydroformylationswithout hydrogenation. For hydroformylation together with hydrogenation,higher H₂/CO ratios are required. These can be obtained by converting,as explained further below.

In general, the partial oxidation is carried out by preheating thehydrocarbons, oxygen and, if appropriate, steam separately from oneanother and introducing them via one or more burners into the upper partof a reactor. The burners allow rapid and intimate mixing of thereactants. The preheated feedstocks react in the absence of catalysts atfrom about 30 to 80 bar and from 1200 to 1500° C. in the combustion zoneof the reactor. The heat generated serves for the steam cracking of thehydrocarbons. The gas leaving the reactor is cooled either directly byquenching with water or indirectly by heat exchange. A small part of thehydrocarbons is usually converted into soot. This is generally removedfrom the synthesis gas by scrubbing with H₂O.

Suitable plants for producing synthesis gas by partial oxidation aredescribed, for example, in Max Appl, loc. cit., p. 106ff.

The above descriptions of steam reforming and partial oxidation applyanalogously to the use of the second butene-depleted C₄-hydrocarbonstream according to the second aspect of the invention.

After-treatment of the Synthesis Gas

A desired carbon monoxide/hydrogen ratio in a synthesis gas can be setby converting over suitable catalysts in the presence of steam.Converting can be employed, in particular, for increasing the H₂/COmolar ratio in a synthesis gas produced by partial oxidation. Theunderlying reaction between carbon monoxide and steam to give carbondioxide and hydrogen is an equilibrium reaction:

CO+H₂O⇄CO₂+H₂

The reaction is exothermic, so that lower temperatures shift theequilibrium to the right-hand side. Converting can be carried out in oneor more stages, e.g. at from 350 to 570° C. and atmospheric pressure orsuperatmospheric pressure, in the presence of catalysts. Suitableconverting catalysts generally comprise Fe—Cr oxide mixtures. Theseallow the CO content to be, if desired, reduced to about 3 to 4% byvolume. In this way, it possible to prepare essentially pure hydrogenwhich is, for example, suitable for the hydrogenation steps of theprocess of the present invention.

Carbon dioxide can be removed by scrubbing with suitable solvents.Suitable methods are, for example, pressure water scrubbing andpotassium carbonate scrubbing. Further advantageous methods are gasscrubbing with monoethanolamine and diethanolamine (cf. Ullmann'sEncyclopedia of Industrial Chemistry, 5th Edition, Volume A12, p. 197).

An overview of suitable methods of removing carbon dioxide may also befound in Max Appl, loc. cit., p. 106ff.

Hydroformylation

Hydroformylation or the oxo process is used to prepare aldehydes fromolefins and synthesis gas, i.e. a mixture of carbon monoxide andhydrogen. The aldehydes obtained can, if desired, be hydrogenated bymeans of hydrogen in the same process step or subsequently in a separatehydrogenation step to form the corresponding alcohols. Thehydroformylation is carried out in the presence of catalysts which arehomogeneously dissolved in the reaction medium. Catalysts used here are,in general, compounds or complexes of metals of transition group VIII,especially Co, Rh, Ir, Pd, Pt or Ru compounds or complexes which can beunmodified or modified with, for example, amine- or phosphine-containingcompounds. A review of processes carried out industrially may be foundin J. Falbe, “New Synthesis with Carbon Monoxide”, Springer-Verlag 1980,page 162ff.

Hydroformylation of Octenes

While short-chain olefins are at present hydroformylated usingpredominantly ligand-modified rhodium carbonyls as catalysts, cobaltassumes a dominant role as catalytically active central atom in the caseof longer-chain olefins, e.g. octenes. This is due, firstly, to the highcatalytic activity of the cobalt carbonyl catalyst regardless of theposition of the olefinic double bonds, the branching structure and thepurity of the olefin to be reacted. Secondly, the cobalt catalyst can beseparated comparatively easily from the hydroformylation products and berecirculated to the hydroformylation reaction. A particularlyadvantageous process for the hydroformylation of octenes comprises

a) bringing an aqueous cobalt(II) salt solution into intimate contactwith hydrogen and carbon monoxide to form a hydroformylation-activecobalt catalyst; bringing the aqueous phase containing the cobaltcatalyst into intimate contact with the octenes together with hydrogenand carbon monoxide in at least one reaction zone, with the cobaltcatalyst being extracted into the organic phase and the octenes beinghydroformylated,

b) treating the output from the reaction zone with oxygen in thepresence of acidic aqueous cobalt(II) salt solution, with the cobaltcatalyst being decomposed to form cobalt(II) salts and the latter beingback-extracted into the aqueous phase; and subsequently separating thephases;

c) returning the aqueous cobalt(II) salt solution to step a).

Suitable cobalt(II) salts are, in particular, cobalt carboxylates, e.g.cobalt(II) formate, cobalt(II) acetate or cobalt ethylhexanoate, andcobalt acetylacetonate. The catalyst formation can be carried outsimultaneously with the catalyst extraction and hydroformylation in onestep in the reaction zone of the hydroformylation reaction or in apreceding step (precarbonylation). Precarbonylation can advantageouslybe carried out as described in DE-A 2 139 630. The resulting aqueoussolution of cobalt(II) salts and cobalt catalyst is then introducedtogether with the octenes to be hydroformylated and hydrogen and carbonmonoxide into the reaction zone. However, in many cases it is preferableto carry out the formation of the cobalt catalyst, the extraction of thecobalt catalyst into the organic phase and the hydroformylation in onestep by bringing the aqueous cobalt(II) salt solution into intimatecontact with the olefins in the reaction zone under hydroformylationconditions. Here, the starting materials are introduced into thereaction zone in such a way that good phase mixing occurs and a veryhigh phase transfer area is generated. Mixing nozzles for multiphasesystems are particularly suitable for this purpose.

After leaving the reaction zone, the reaction mixture is depressurizedand passed to the cobalt removal step. In the cobalt removal step, thereaction mixture is freed of cobalt carbonyl complexes by means of airand oxygen in the presence of aqueous, slightly acidic cobalt(II) saltsolution. In the cobalt removal step, the hydroformylation-active cobaltcatalyst is decomposed to form cobalt(II) salts. The cobalt(II) saltsare back-extracted into the aqueous phase. The aqueous cobalt(II) saltsolution can subsequently be returned to the reaction zone or thecatalyst formation step.

The crude hydroformylation product can be fed directly to thehydrogenation step, or, alternatively, the pure C₉-aldehydes can beisolated by known methods, e.g. by distillation.

Hydroformylation of Butenes

The second aspect of the invention provides for the hydroformylation ofpart of the butenes present in the C₄-hydrocarbon stream used, beforethe butene-depleted C₄-hydrocarbon stream obtained here (also referredto as “first butene-depleted C₄-hydrocarbon stream” to distinguish itfrom other butene-depleted C₄-hydrocarbon streams occurring in theprocess of the present invention) is passed to butene dimerization.

The hydroformylation of a hydrocarbon stream comprising 1-butene,2-butene and possibly isobutene gives C₅-aldehydes, i.e.n-valeraldehyde, 2-methylbutanal and possibly 2,2-dimethylpropanal. Thebutene hydroformylation is preferably carried out in the presence of arhodium catalyst complex in conjunction with a triorganophosphineligand. The triorganophosphine ligand can be a trialkylphosphine such astributylphosphine, an alkyldiarylphosphine such asbutyldiphenylphosphine or an aryldialkylphosphine such asphenyldibutylphosphine. However, particular preference is given totriarylphosphine ligands such as triphenylphosphine,tri-p-tolylphosphine, trinaphthylphosphine, phenyldinaphthylphosphine,diphenylnaphthylphosphine, tri(p-methoxyphenyl)phosphine,tri(p-cyanophenyl)phosphine, tri(p-nitrophenyl)phosphine,p-N,N-dimethylaminophenylbisphenylphosphine and the like.Triphenylphosphine is most preferred.

The butene hydroformylation is preferably carried out under conditionsunder which the reaction of 1-butene occurs quickly while thehydroformylation of 2-butene and isobutene occurs slowly. In this way,it is possible for essentially only 1-butene to be converted inton-valeraldehyde and 2-methylbutanal in the hydroformylation.while the2-butene and any isobutene present are recovered essentially unchanged.This gives a butene-depleted C₄-hydrocarboh stream whose 1-butenecontent is reduced compared to the C₄-hydrocarbon stream used and whichcomprises essentially the original amounts of 2-butene and isobutenewhich were present in the C₄-hydrocarbon stream used. The ratio ofn-valeraldehyde to 2-methylbutanal in the C₅-aldehydes obtained ispreferably at least 4:1, in particular at least 8:1.

The preferential hydroformylation of 1-butene over 2-butene andisobutene can be achieved by using a large excess of triorganophosphorusligands and by careful control of the temperatures and partial pressuresof the reactants and/or products. Thus, the triorganophosphine ligand ispreferably used in an amount of at least 100 mol per gram atom ofrhodium. The temperature is preferably in the range from 80 to 130° C.,the total pressure is preferably not more than 5000 kPa and the partialpressure-of carbon monoxide is kept below 150 kPa and that of hydrogenis kept in the range from 100 to 800 kPa. A suitable hydroformylationprocess in which a mixture of butenes is used is described in EP 0 016286.

Hydrogenation

The hydrogenation of the C₉-aldehydes to form the C₉-alcohols can inprinciple be carried out using the same catalysts as in thehydroformylatibn, usually at higher temperature. However, preference isgenerally given to more selective hydrogenation catalysts which are usedin a separate hydrogenation step. Suitable hydrogenation catalysts aregenerally transition metals such as Cr, Mo, W, Fe, Rh, Co, Ni, Pd, Rt,Ru, etc., or mixtures thereof which can be applied to supports, e.g.activated carbon, aluminum oxide, kieselguhr,.etc., to increase theactivity and stability. To increase the catalytic activity, Fe, Co andpreferably Ni can also be used in the form of the Raney catalysts, viz.as metal sponge having a very high surface area. The hydrogenation ofthe C₉-aldehydes is carried out under conditions which depend on theactivity of the catalyst, preferably at elevated temperatures andsuperatmospheric pressure. The hydrogenation temperature is preferablyfrom about 80 to 250° C., while the pressure is preferably from about 50to 350 bar.

The crude hydrogenation product can be worked up by customary methods,e.g. by distillation, to give the C₉-alcohols.

The hydrogen required for the hydrogenation preferably originates atleast in part from the synthesis gas obtained by steam reforming orpartial oxidation of the butene-depleted C₄-hydrocarbon stream. Thehydrogen can be isolated by methods known per se, for example pressureswing adsorption (PSA) or low-temperature distillation (cf. Max Appl,loc. cit., p. 108ff).

Aldol Condensation

Two molecules of C₅-aldehyde can be condensed to form α,β-unsaturatedC₁₀-aldehydes, in particular 2-propyl-2-heptenal and2-propyl-4-methyl-2-hexenal. The aldol condensation is carried out in amanner known per se, e.g. by action of an aqueous base such as sodiumhydroxide or potassium hydroxide. As an alternative, it is also possibleto use a heterogeneous basic catalyst such as magnesium oxide and/oraluminum oxide (cf. for example, EP-A 792 862).

The product of the aldol condensation is then catalytically hydrogenatedby means of hydrogen to form C₁₀-alcohols, in particular2-propylheptanol and 2-propyl-4-methylhexanol. The above description ofthe hydrogenation of the C₉-aldehydes applies analogously to thehydrogenation of the aldol condensation products.

The invention will now be illustrated by the following examples, whichare partly based on simulation calculations. The simulation calculationswere carried out using the ASPENPLUS simulation program from ASPEN Tech.By means of this simulation program, the thermodynamic equilibriumestablished during steam reforming or partial oxidation of a givenhydrocarbon stream under particular conditions was calculated. Thethermodynamic equilibrium is generally achieved approximately when usingcatalysts as are employed in industrial practice. The simulation wascarried out on the bases of process temperatures and pressures as arecustomarily employed in the steam reforming or partial oxidation ofhydrocarbons.

EXAMPLE 1

A C₄-hydrocarbon stream comprising 88 mol % of butene and 12 mol % ofbutane is passed at 20 bar and 80° C. over a catalyst bed in anadiabatic reactor (length: 4 m, diameter: 80 cm). The catalyst had beenproduced as described in DE 4 339 713 in the form of pellets havingdimensions of 5×5 mm (composition in mol % of active components: Nio 50mol %, TiO₂ 12.5 mol %, SiO₂ 33.5 mol %, Al₂O₃ 4 mol %).

The octenes and higher butene oligomers formed were separated from theoutput from the reactor. The resulting butene-depleted C₄-hydrocarbonmixture comprised 80.5 mol % of butane and 19.5 mol % of butene,corresponding to a butene conversion of 95%.

In a simulation calculation, the synthesis gas composition expected inthe steam reforming of this butene-depleted C₄-hydrocarbon stream wascalculated. The following parameters were employed:

S/C =2.5

(S/C=mol of steam used for steam reforming per mol of C present in theC₄ feed mixture)

Reformer outlet temperature=880° C

CO₂ recycle=100%

Pressure=20 bar absolute

Hydrocarbon feed: Composition: 80.5 mol % of butane 19.5 mol % of buteneMass flow: 57,730 kg/h Inlet temperature: 500° C. Steam: Mass flow:180,152 kg/h Inlet temperature: 500° C. Recirculated CO₂: Mass flow:107,833 kg/h

The results of the simulation calculation are as follows:

Reformer Outlet:

Mass flow: 345,716 kg/h Composition: CO 18.0 mol % CO₂ 11.8 mol % CH₄1.4 mol % H₂ 38.4 mol % H₂O 30.4 mol % butane 0.0 mol % butene 0.0 mol %

Synthesis gas after CO₂ scrub:

Mass flow: 124,629 kg/h Composition: CO 31.1 mol % CO₂ 0.0 mol % CH₄ 2.4mol % H₂ 66.5 mol % H₂O 0.0 mol % butane 0.0 mol %

The H₂/CO molar ratio is 2.14. A synthesis gas of this composition iswell suited to the hydroformylation and hydrogenation by customarymethods of the olefins obtained according to the above description. TheCH₄ Content of the synthesis gas of 2.4 mol % is not a problem in thehydroformylation.

EXAMPLE 2

Example 1 was repeated, but the simulation was carried out for a partialoxidation of the butene-depleted C₄-hydrocarbon stream. The followingparameters were used as a basis: temperature 1200° C., pressure 50 bar,no CO₂ recycle.

Hydrocarbon feed: Composition: 80.5 mol % of butane 19.5 mol % of buteneMass flow: 57,730 kg/h Temperature: 300° C. Steam: Mass flow: 36,200kg/h Temperature: 270° C. Oxygen: Mass flow: 46,703 kg/h Temperature:25° C.

The simulation gave the following results:

Reactor Outlet:

Composition: 32.7 mol % of CO 4.2 mol % of CO₂ 0.35 mol % of CH₄, 47.5mol % of H₂ 15.2 mol % of H₂O 0.0 mol % of butane 0.0 mol % of butene0.0 mol % of O₂ Mass flow: 158,635 kg/h Temperature: 1200° C. Pressure:50 bar

The H₂/CO molar ration is 1.455.

In addition, the synthesis gas composition of the above gas afterhigh-temperature converting was simulated. The simulation was based on91,646 kg/h of the above-described gas leaving the reactor outlet beingconveyed in a bypass around high-temperature converting and theremainder being subjected to high-temperature converting. The simulationgave the following result:

Synthesis gas after high-temperature converting:

Composition: 28.1 mol % of CO 8.8 mol % of CO₂ 0.35 mol % of CH₄ 52.0mol % of H₂ 10.7 mol % of H₂O 0.0 mol % of butane 0.0 mol % of butene0.0 mol % of O₂

The H₂/CO molar ratio of the synthesis gas after high-temperatureconverting is 1.85. Varying the amount passed through the bypass makesit possible to achieve other H₂/CO ratios, so that the synthesis gascomposition can be optimally matched to the hydroformylation and/orhydrogenation of the olefins obtained according to the abovedescription.

We claim:
 1. A process for preparing C₉-alcohols, which comprises a)providing a C₄-hydrocarbon stream comprising butene and butane; b)subjecting the C₄-hydrocarbon stream to oligomerization over an olefinoligomerization catalyst and fractionating the resulting reactionmixture to give an octene-containing stream and a butene-depletedC₄-hydrocarbon stream; c) subjecting the butene-depleted C₄-hydrocarbonstream to steam reforming or partial oxidation to give carbon monoxideand hydrogen; d) hydroformylating the octene-containing stream by meansof carbon monoxide and hydrogen in the presence of a hydroformylationcatalyst to form C₉-aldehydes, where the carbon monoxide used and/or thehydrogen used originate at least in part from step c); and e)catalytically hydrogenating the C₉-aldehydes by means of hydrogen.
 2. Aprocess as claimed in claim 1, wherein the hydrogen used in step e)originates at least in part from step c).
 3. A process as claimed inclaim 1, wherein the butene-depleted C₄-hydrocarbon stream is fully orpartially hydrogenated prior to steam reforming.
 4. A process as claimedin claim 1, wherein the steam reforming includes the use of aprereformer.
 5. A process as claimed in claim 1, wherein the mixture ofcarbon monoxide and hydrogen obtained by steam reforming or partialoxidation of the butene-depleted C₄-hydrocarbon stream is subjected tohigh-temperature converting.
 6. A process as claimed in claim 1, whereinthe C₄-hydrocarbon stream contains from 50 to 99 mol % of butene.
 7. Aprocess as claimed in claim 1, wherein the butene-depletedC₄-hydrocarbon stream contains from 5 to 70 mol % of butene.
 8. Aprocess as claimed in claim 1, wherein the olefin oligomerizationcatalyst is a heterogeneous, nickel-containing catalyst.
 9. A processfor the integrated preparation of C₉-alcohols and C₁₀-alcohols, whichcomprises a) providing a C₄-hydrocarbon stream comprising butene andbutane; b) hydroformylating the C₄-hydrocarbon stream by means of carbonmonoxide and hydrogen to form C₅-aldehydes, so as to give a firstbutene-depleted C₄-hydrocarbon stream; c) subjecting the C₅-aldehydes toan aldol condensation; and d) catalytically hydrogenating the productsof the aldol condensation by means of hydrogen to form C₁₀-alcohols; e)subjecting the first butene-depleted C₄-hydrocarbon stream tooligomerization over an olefin oligomerization catalyst andfractionating the resulting reaction mixture to give anoctene-containing stream and a second butene-depleted C₄-hydrocarbonstream; f) hydroformylating the octene-containing stream by means ofcarbon monoxide and hydrogen in the presence of a hydroformylationcatalyst to form C₉-aldehydes; g) catalytically hydrogenating theC₉-aldehydes by means of hydrogen; h) subjecting the secondbutene-depleted C₄-hydrocarbon stream to steam reforming or partialoxidation to give carbon monoxide and hydrogen which are recirculated atleast in part to step b) and/or step f).
 10. A process as claimed inclaim 9, wherein the hydrogen used in step d) and/or step g) originatesat least in part from step h).
 11. A process as claimed in claim 9,wherein the second butene-depleted C₄-hydrocarbon stream is fully orpartially hydrogenated prior to steam reforming.
 12. A process asclaimed in claim 9, wherein the steam reforming includes the use of aprereformer.
 13. A process as claimed in claim 9, wherein the mixture ofcarbon monoxide and hydrogen obtained by steam reforming or partialoxidation of the second butene-depleted C₄-hydrocarbon stream issubjected to high-temperature converting.
 14. A process as claimed inclaim 9, wherein the C₄-hydrocarbon contains from 50 to 99 mol % ofbutene.
 15. A process as claimed in claim 9, wherein the olefinoligomerization catalyst is a heterogeneous, nickel-containing catalyst.